Photoelectric conversion element and process for fabricating the same, electronic apparatus and process for fabricating the same, and semiconductor layer and process for forming the same

ABSTRACT

A paste in which semiconductor fine grain such as titanium oxide fine grain or the like and a binder made of a polymer compound are mixed is coated onto a transparent conductive substrate and sintered, thereby forming a semiconductor layer made of the semiconductor fine grain, after that, ultraviolet rays are irradiated to the semiconductor layer and, by using a photocatalyst effect of the semiconductor fine grain, an organic substance remaining in the semiconductor layer is removed.

TECHNICAL FIELD

The invention relates to a photoelectric conversion device, itsmanufacturing method, an electronic apparatus, its manufacturing method,a semiconductor layer, and its manufacturing method and is suitable whenit is applied to, for example, a photoelectric conversion device using asemiconductor layer made of semiconductor fine grain, particularly, asemiconductor layer made of semiconductor fine grain sensitized by dye.

BACKGROUND ART

Since a solar cell as a photoelectric conversion device to convertsunlight into an electric energy uses the sunlight as an energy source,an influence that is exercises to the global environment is extremelysmall and it is expected to be spread further.

Various materials have been examined as a material of the solar cell anda number of solar cells using silicon have been commercialized. They aremainly classified into: a crystalline silicon solar cell using singlecrystal silicon or poly crystal silicon; and an amorphous silicon solarcell. Hitherto single crystal silicon or poly crystal silicon, that is,crystalline silicon has often been used for the solar cells.

However, in the crystalline silicon solar cell, although photoelectricconversion efficiency indicative of performance of converting the light(solar) energy into the electric energy is higher than that of theamorphous silicon solar cell, since a large energy and a long time arerequired for a crystal growth, productivity is low and it isdisadvantageous in terms of costs.

Although higher light absorptivity, wider selecting range of asubstrate, easier realization of a large area, and the like arecharacteristics of the amorphous silicon solar cell than in the case ofthe crystalline silicon solar cell, the photoelectric conversionefficiency is lower than that of the crystalline silicon solar cell.Further, in the amorphous silicon solar cell, although the productivityis higher than that of the crystalline silicon solar cell, a vacuumprocess is necessary upon manufacturing in a manner similar to thecrystalline silicon solar cell and a facility related cost is stillheavy.

In order to solve the above problems and realize the even lower costs ofthe solar cell, solar cells using an organic material in place of asilicon material have been studied for a long time. However, since mostof those solar cells have the low photoelectric conversion efficiency ofabout 1%, they are not put into practical use.

Among them, according to the dye sensitized solar cell proposed byGlötzl et al. in 1991, since it is reasonable in price, shows the highphotoelectric conversion efficiency and, unlike the conventional siliconsolar cell, a large apparatus is unnecessary upon manufacturing, and thelike, attention has been paid (for example, Nature, 353, p. 737 (1991)).

According to a general structure of such a dye sensitized solar cell, asemiconductor porous electrode in which a sensitizing dye is combinedwith a semiconductor porous membrane of a titanium oxide or the likeformed on a transparent conductive substrate and a counter electrodeobtained by forming a platinum layer or the like onto the substrate arecombined, and an organic electrolytic solution containing redox speciessuch as iodine, iodide ions, or the like is filled between bothelectrodes.

The semiconductor porous electrode which is used can be obtained by amethod whereby semiconductor fine grain (titanium oxide fine grain orthe like) and a polymer compound such as polyethylene glycol,polystyrene, or the like serving as a binder are mixed, coated onto thetransparent conductive substrate by a doctor blade method, a spincoating method, a dip coating method, or the like, and thereafter,sintered at temperatures of 400 to 500° C. for 30 minutes to one hour.The semiconductor porous electrode is constructed by a semiconductorlayer (or semiconductor thin film) made of semiconductor fine grainhaving a fine grain diameter of about 20 to 30 nm and has a structure inwhich many fine holes in that a diameter of tens of nm is set to thecenter of distribution exist in the electrode. The titanium oxide porouselectrode as a semiconductor porous electrode suitable for thephotoelectric conversion device among them is an anatase-type fine grainthin film in which a grain diameter is small, a specific surface area islarge, and a photocatalyst activity is high.

It has been reported that if the semiconductor fine grain is made of thetitanium oxide, its surface changes to the surface having hydrophilicity(surface hydroxyl group increases) by irradiating ultraviolet rays(Nature, 388, p. 431 (1999)).

However, according to the knowledge obtained uniquely by the inventorset al. of the present invention, it has been found that if a sinteringtemperature is lowered or a sintering time is shortened in order tosuppress the crystal growth and keep the crystal grain diameter small, alarge amount of organic substance derived from the polymer compound usedas a binder remains in the semiconductor porous electrode. Thisobstructs combination of the semiconductor fine grain, resulting indeterioration of the photoelectric conversion efficiency. On thecontrary, if the sintering temperature is raised or the sintering timeis extended in order to reduce the residual amount of the organicsubstance, the crystal grain diameter increases, the specific surfacearea decreases, and the structure changes to the crystalline structurein which the photocatalyst activity is low (in the case of titaniumoxide, rutile type). Also in this case, the photoelectric conversionefficiency deteriorates.

Therefore, the problem to be solved by the invention is to provide aphotoelectric conversion device which has such a crystalline structure(for example, an anatase type in the case of titanium oxide) that anamount of residual organic substance in a semiconductor layer made ofsemiconductor fine grain is extremely small, a crystal grain diameter ofthe semiconductor layer is small, a specific surface area is large, anda photocatalyst activity is high and whose photoelectric conversionefficiency is high and to provide a manufacturing method of such adevice.

More generally, the problem to be solved by the invention is to providean electronic apparatus which has such a crystalline structure that anamount of residual organic substance in a semiconductor layer made ofsemiconductor fine grain is extremely small, a crystal grain diameter ofthe semiconductor layer is small, a specific surface area is large, anda photocatalyst activity is high and whose characteristics are excellentand to provide a manufacturing method of such an electronic apparatus.

DISCLOSURE OF INVENTION

To solve the above problem, according to the first invention of theinvention, there is provided a manufacturing method of a photoelectricconversion device, whereby a paste in which semiconductor fine grain anda binder made of a polymer compound are mixed is coated onto atransparent conductive substrate and sintered, thereby forming asemiconductor layer made of the semiconductor fine grain,

wherein after the semiconductor layer is formed, ultraviolet rays areirradiated to the semiconductor layer and, by using a photocatalysteffect of the semiconductor fine grain, an organic substance remainingin the semiconductor layer is removed.

According to the second invention of the invention, there is provided aphotoelectric conversion device using a semiconductor layer made ofsemiconductor fine grain,

wherein a paste in which the semiconductor fine grain and a binder madeof a polymer compound are mixed is coated onto a transparent conductivesubstrate and sintered, thereby forming the semiconductor layer made ofthe semiconductor fine grain, after that, ultraviolet rays areirradiated to the semiconductor layer and, by using a photocatalysteffect of the semiconductor fine grain, an organic substance remainingin the semiconductor layer is removed.

According to the third invention of the invention, there is provided aphotoelectric conversion device using a semiconductor layer made ofsemiconductor fine grain,

wherein an organic substance does not substantially remain in thesemiconductor layer.

Specific examples of the residual amount of the organic substance in thesemiconductor layer will be mentioned. In general, a content of a carboncompound of the semiconductor layer is equal to 1 atom % or less,preferably, 0.6 atom % or less, more preferably, 0.3 atom % or less, andfurther preferably, 0.1 atom % or less.

In the first to third inventions, it is desirable that the semiconductorfine grain is a semiconductor which causes holes or active oxygenspecies trapped on the surface under the light excitation and exhibitsthe photocatalyst activity. One kind or two or more kinds ofsemiconductor fine grain showing the photocatalyst activity are used.Specifically speaking, the semiconductor fine grain showing thephotocatalyst activity comprises, for example, titanium oxide(particularly preferably, titanium oxide having a crystalline structureof the anatase type), zinc oxide, strontium titanate, or the like.

Although the grain diameter of the semiconductor fine grain is notparticularly limited, it is preferable to set the mean grain diameter ofthe primary particle to 1 to 200 nm, particularly preferably, 5 to 100nm. It is also possible to mix semiconductor fine grain whose mean graindiameter is larger than such a mean grain diameter to the semiconductorfine grain of such a mean grain diameter, scatter incident light by thesemiconductor fine grain of large mean grain diameters, and improvequantum efficiency. In this case, it is desirable that the mean graindiameter of the semiconductor fine grain to be additionally mixed isequal to 20 to 500 nm.

Generally, the more a thickness of semiconductor layer comprising thesemiconductor fine grain increases, the more an amount of adsorbed dyeper unit projection area increases, so that a capturing ratio of thelight rises. However, since a diffusion length of the injected electronsincreases, a loss caused by charge recombination also increases.Therefore, although a preferable thickness of semiconductor layerexists, it is generally equal to 0.1 to 100 μm, preferably, 1 to 50 μm,particularly preferably, 3 to 30 μm. To increase a surface area of thesemiconductor fine grain, remove impurities of the semiconductor layermade of the semiconductor fine grain, and raise electron injectingefficiency upon injecting electrons from the dye into the semiconductorfine grain, for example, a chemical process using a titaniumtetrachloride aqueous solution or an electrochemical process using atitanium trichloride aqueous solution can be also performed. Aconductive assistant can be also added to reduce an impedance of thesemiconductor layer made of the semiconductor fine grain.

It is preferable that the binder made of the polymer compound to beadded to the paste is insoluble to a dye solution upon dye dyeing or anelectrolyte. However, if the binder can be preliminarily removed bysintering or irradiating the ultraviolet rays, the binder is not alwaysnecessary to be insoluble. A well-known compound can be used as apolymer compound. Although a cellulose, a polyether, polyvinyl alcohol,polyacrylic acid, polyacrylamide, polyethylene glycol, polystyrene,polyethylene imine, poly(metha)methyl acrylate, polyvinylidene fluoride,styrene-butadiene rubber, polyamideimide, polytetrafluoroethylene(fluororesin), and the like can be mentioned, the invention is notlimited to them. Two or more kinds of them can be also mixed and used. Acompound superior in improving viscosity is preferable as a polymercompound. Specifically speaking, polyethylene glycol, polystyrene, orthe like can be mentioned.

Although a manufacturing method of the paste in which the semiconductorfine grain and the binder made of the polymer compound have been mixedis not particularly limited, a wet-type film forming method ispreferable in consideration of physical property, use efficiency,manufacturing costs, and the like and a method whereby powder or sol ofthe semiconductor fine grain is uniformly distributed into a solventsuch as water or the like, the binder is further added thereto, and thepaste is adjusted and coated onto the transparent conductive substrate.A coating method is not particularly limited and the coating process canbe performed by a well-known method. For example, it can be performed bythe following various methods: a dipping method; a spraying method; awire bar method; a spin coating method; a roller coating method; a bladecoating method; a gravure coating method; and a wet-type printing methodsuch as anastatic printing, offset, gravure, copperplate printing,rubber printing, screen printing, and the like. A commercially availablepowder, sol, or slurry can be used as anatase-type titanium oxide or theanatase-type titanium oxide having a predetermined grain diameter can bealso formed by a well-known method whereby titanium oxide alkoxide ishydrolyzed or the like. In the case of using the commercially availablepowder, it is preferable to dissolve the secondary aggregation of theparticles and it is desirable to mill the particles by using a mortar, aball mill, or the like at the time of the adjustment of a coatingliquid. At this time, to prevent that the particles whose secondaryaggregation has been dissolved is reaggregated, acetyl acetone, acidsuch as hydrochloric acid, nitric acid, or the like, alkali, a surfaceactive agent, a chelating agent, or the like can be added.

After coating the paste in which the semiconductor fine grain and thebinder made of the polymer compound have been mixed, ordinarily, thepaste is dried in order to remove the solvent contained in the paste. Adrying temperature is equal to or lower than a boiling point of thesolvent and is generally set to, for example, about 50° C. when thesolvent is a water and to about 80° C. when the solvent is an organicsolvent.

As ultraviolet rays to be irradiated to the semiconductor layer, theultraviolet rays having an arbitrary wavelength can be fundamentallyused so long as its photon energy is equal to or higher than a band gapenergy of the semiconductor fine grain which is used. As a light sourceof the ultraviolet rays, any light source can be fundamentally used. Anyone of a lamp light source, a semiconductor light source (semiconductorlaser, light emitting diode), laser light source (excimer laser or thelike) other than the semiconductor laser, and the like can be used.Specifically speaking, ultraviolet rays (wavelength is equal to 254 nm,303 nm, 313 nm, 365 nm, or the like: mainly, 365 nm) by an extra-highpressure mercury lamp or the like can be given.

The dye to be adsorbed to the semiconductor fine grain is notparticularly limited so long as it has a charge separating function andshows a sensitizing function. For example, there can be mentioned: anxanthene-based dye such as rhodamine B, rose bengal, eosin, Erythrocin,or the like; a cyanine-based dye such as quinocyanine, cryptcyanine, orthe like; a basic dye such as phenosafranine, Capri blue, thiocin,methylene blue, or the like; a porphyrin-based compound such aschlorophyll, zinc porphyrin, magnesium porphyrin, or the like; azo dye;a phthalocyanine compound; a coumalin-based compound; a complex compoundsuch as ruthenium (Ru) tris bipyridyl, or the like; anthraquinone-baseddye; a polycyclic quinone-based dye; a coumalin-based dye; etc. Amongthem, although the Ru tris bipyridyl complex compound is particularlypreferable since its quantum efficiency is high, the invention is notlimited to it. One of those dyes can be solely used or a combinationobtained by mixing two or more kinds of those dyes can be used.

An adsorbing method of the dye to the semiconductor fine grain is notparticularly limited. For example, there is generally used a methodwhereby the dye is dissolved into a solvent such as alcohols, nitryls,nitromethane, hydrocarbon halide, ether, dimethyl sulfoxide, amides,N-methylpyrrolidone, 1,3-dimethyl imidazolidinone, 3-methyloxazolidinone, ester, carbonates, ketones, hydrocarbon, water, or thelike and the semiconductor layer made of the semiconductor fine grain isdipped into the resultant solvent or the semiconductor layer made of thesemiconductor fine grain is coated with a dye solution. In this case, anamount of dye molecules into one semiconductor fine grain is equal to 1to 1000 molecules and, further preferably, 1 to 100 molecules. When thedye molecules are remarkably and excessively adsorbed to thesemiconductor fine grain, the electrons excited by the light energy arenot injected into the semiconductor fine grain but reduce theelectrolyte, so that they become a cause for the energy loss. Therefore,as for the dye molecules, monomolecular adsorption to the semiconductorfine grain is in an ideal state and a temperature and a pressure foradsorbing them can be changed as necessary. A carboxylic acid such asdeoxycholic acid or the like can be also added to reduce aggregation ofthe dyes. An ultraviolet ray absorbent can be also used together withit.

To promote the removal of the dyes which have excessively been adsorbed,the surface of the semiconductor layer made of the semiconductor finegrain on which the dyes have been adsorbed can be also processed byusing an organic substance such as amines, acetonitrile, or the like.Pyridine, 4-tert-butyl pyridine, polyvinyl pyridine, or the like can begiven as an example of the amines. If each of them is in a liquid state,it can be used as it is or can be dissolved into an organic solvent andused.

As a transparent conductive substrate, it can be realized by forming atransparent electrode (transparent conductive film) onto a conductive ornon-conductive transparent supporting substrate or can be realized byforming a transparent substrate which is conductive as a whole. Amaterial of the transparent supporting substrate or the transparentsubstrate is not particularly limited and various base materials can beused so long as they are transparent or they are transparent and havethe conductivity. As a transparent supporting substrate or a transparentsubstrate, it is preferable to use a substrate which is excellent interms of shutdown performance against the moisture or gases which enterfrom an outside of the photoelectric conversion device, durabilityagainst solvents and circumstances, and the like. Specifically speaking,there can be mentioned: a transparent inorganic substrate such asquartz, glass, or the like; and a transparent plastic substrate made ofpolyethylene telephthalate, polyethylene naphthalate, polycarbonate,polystyrene, polyethylene, polypropylene, polyphenylene sulfide,polyvinylidene fluoride, tetraacetylcellulose, phenoxy bromide, aramids,polyimides, polystyrenes, polyarylates, polysulfones, polyolefins, orthe like. However, the invention is not limited to them. From viewpointsof workability, light-weight performance, and the like, it is preferableto use the transparent plastic substrate as a transparent supportingsubstrate or a transparent substrate. A thickness of transparentsupporting substrate or transparent substrate is not particularlylimited and an arbitrary value can be selected in dependence on lighttransmittance, the shutdown performance between the inside and theoutside of the photoelectric conversion device, and the like.

A smaller sheet resistance of the transparent conductive substrate isbetter. Specifically speaking, the sheet resistance of the transparentconductive substrate is preferably set to 500 Ω/cm² or less, morepreferably, 10 Ω/cm² or less. In the case of forming the transparentelectrode onto the transparent supporting substrate, any type ofmaterial can be fundamentally used so long as it has the conductivityand transparency. However, it is desirable to use indium-tin compositeoxide (ITO), fluorine doped SnO₂ (FTO), SnO₂, or the like from aviewpoint that they have the conductivity, transparency, and further,heat resistance at high levels. ITO is preferable among them inconsideration of the costs. It is also possible to combine two or morekinds of those materials and use them. To reduce the sheet resistance ofthe transparent conductive substrate and improve the collectingefficiency, metal wirings having the high conductivity can be alsopatterned onto the transparent conductive substrate.

An arbitrary electrode can be used as a counter electrode so long as itis made of a conductive substance. An insulative substance can be alsoused so long as a conductive layer is formed on the side where it facesthe semiconductor layer. However, it is desirable that a material whichis electrochemically stable is used as an electrode material.Specifically speaking, it is preferable to use platinum, gold,conductive polymer, carbon, or the like. To improve the catalyst effectof the redox reaction, it is desirable that the electrode on the sidewhere it faces the semiconductor layer has a fine structure and itssurface is increased. For example, in the case of platinum, it isdesirable to be in the platinum black state and in the case of carbon,it is desirable to be in the porous state. The platinum black state canbe formed by an anode oxidizing method, a platinum chloride acidtreatment, or the like of platinum. Carbon in the porous state can beformed by a method of sintering carbon fine grain, a method of sinteringan organic polymer, or the like.

The electrolyte becomes a carrier transfer layer and is constructed by aredox species and a solvent. Specifically speaking, the redox species isconstructed by, for example, a combination of iodine (I₂) and an iodinecompound (metal iodide, organic iodide, or the like) or a combination ofbromine (Br₂) and a bromine compound (metal bromide, organic bromide, orthe like). Further, there can be used: metal complexes such asferrocianic acid salt/ferricianic acid salt, ferrocene/ferricynium ions,or the like; sulfur compounds such as polysodium sulfide,alkylthiol/alkyl disulfide, or the like; viologen dye;hydroquinone/quinone; or the like. As cations of the above metalcompound, it is suitable to use Li, Na, K, Mg, Ca, Cs, etc. As cationsof the above organic compound, it is suitable to use a quaternaryammonium compound such as tetraalkyl ammoniums, pyridinums,imidazoliums, or the like. However, the cations are not limited to themand it is also possible to combine two or more kinds of those elementsand use the mixture as necessary. Among them, an electrolyte obtained bycombining I₂ with quaternary ammonium compound such as LiI, NaI,imidazolium iodide, or the like is suitable. A concentration ofelectrolyte salt is preferably set to 0.05 to 5 M for the solvent and,further preferably, 0.2 to 1 M. A concentration of I₂ or Br₂ ispreferably set to 0.0005 to 1 M and, further preferably, 0.0001 to 0.1M. To improve a release voltage and a short-circuit current, variousadditives such as 4-tert-butyl pyridine, 2-n-propyl pyridine, carboxylicacid, and the like can be also added.

As a solvent constructing the electrolyte compositions mentioned above,the following elements can be mentioned: water; an alcohol; an ether;ester; a carbonate; a lactone; a carboxylic acid ester; a triesterphosphate; a heterocyclic compound; a nitrile; a ketone; an amide;nitromethane; halogenated hydrocarbon; dimethylsulfoxide; sulfolane;N-methyl pyrolidone; 1,3-dimethyl imidazolidinone; 3-methyloxazolidinone; hydrocarbon; and the like. However, the invention is notlimited to them and one kind of those elements can be solely used or twoor more kinds of those elements can be mixed and used. A roomtemperature ionic liquid of a quaternary ammonium salt of a tetraalkyl,a pyridinium, or an imidazolium can be also used as a solvent.

To reduce a leakage liquid of the photoelectric conversion device andvolatilization of the electrolyte, gelatinizer, polymer, cross linkingmonomer, or the like is dissolved in the electrolyte compositions andcan be used as a gel electrolyte. As for a ratio of a gel matrix and theelectrolyte compositions, if an amount of electrolyte compositions islarge, ion conductivity increases but a mechanical strength decreases.On the contrary, if the amount of electrolyte compositions is too small,although the mechanical strength is large, the ion conductivitydecreases. Therefore, it is desirable that the amount of electrolytecompositions is equal to 50 to 99 wt % of the gel electrolyte and, morepreferably, 80 to 97 wt %. The photoelectric conversion device of atotal solid type can be also realized by dissolving the electrolyte anda plasticizer into the polymer and volatilizing and removing theplasticizer.

Although a manufacturing method of the photoelectric conversion deviceis not particularly limited, for example, the electrolyte compositionscan be in the liquid state or can be gelatinized in the photoelectricconversion device. If the electrolyte compositions is in the liquidstate before introduction, the semiconductor layer and the counterelectrode are allowed to face each other and the substrate portion inwhich the semiconductor layer is not formed is sealed lest the twoelectrodes are come into contact with each other. At this time, althougha gap between the semiconductor layer and the counter electrode is notparticularly limited, it is ordinarily set to 1 to 100 μm and, morepreferably, 1 to 50 μm. If a distance between the electrodes is toolong, the photocurrent decreases due to the decrease of theconductivity. Although a sealing method is not particularly limited, amaterial having light resistance, insulation resistance, and moistureresistance is preferable, various welding methods, an epoxy resin, anultraviolet curing resin, an acrylic adhesive agent, EVA (ethylene-vinylacetate), an ionomer resin, ceramics, a heat melt-bonding film, and thelike can be used. Although an injection port to inject the solution ofthe electrolyte compositions is necessary, a location of the injectionport is not particularly limited so long as it is not arranged on thesemiconductor layer and the counter electrode in the portion which facesit. Although a liquid injecting method is not particularly limited, amethod of injecting the liquid into the cell which has previously beensealed and in which the injection port of the solution is opened ispreferable. In this case, a method of dropping a few droplets of thesolution into the injection port and injecting the liquid by a capillarytube phenomenon is simple. The liquid injecting operation can be alsoperformed under a reduced pressure or a heating state as necessary.After the solution is completely injected, the solution remaining in theinjection port is removed and the injection port is sealed. This sealingmethod is not particularly limited as well and a glass plate or aplastic substrate can be also adhered and sealed with a sealing agent asnecessary. In the case of the gel electrolyte using polymer or the likeor the electrolyte of a total solid type, the polymer solutioncontaining the electrolyte compositions and plasticizer is volatilizedand removed by a casting method on the semiconductor electrode adsorbingthe dye. After the plasticizer is completely removed, the sealing isperformed in a manner similar to that mentioned above. It is preferableto perform the sealing under an inert gas atmosphere or in the reducedpressure by using a vacuum sealer or the like. After the sealing isperformed, the heating and pressurizing operations can be also performedas necessary in order to sufficiently dip the electrolyte into thesemiconductor layer.

The photoelectric conversion devices can be manufactured in variousshapes in accordance with the application and their shapes are notparticularly limited.

The method whereby after the semiconductor layer made of thesemiconductor fine grain is formed, the ultraviolet rays are irradiatedto the semiconductor layer and, by using the photocatalyst effect of thesemiconductor fine grain, the organic substance remaining in thesemiconductor layer is removed can be applied not only to thephotoelectric conversion device but also all electronic apparatuses eachusing the semiconductor layer made of the semiconductor fine grain.

According to the fourth invention of the invention, there is provided amanufacturing method of an electronic apparatus, whereby a paste inwhich semiconductor fine grain and a binder made of a polymer compoundare mixed is coated onto a substrate and sintered, thereby forming asemiconductor layer made of the semiconductor fine grain,

wherein after the semiconductor layer is formed, ultraviolet rays areirradiated to the semiconductor layer and, by using a photocatalysteffect of the semiconductor fine grain, an organic substance remainingin the semiconductor layer is removed.

According to the fifth invention of the invention, there is provided anelectronic apparatus using a semiconductor layer made of semiconductorfine grain,

wherein a paste in which the semiconductor fine grain and a binder madeof a polymer compound are mixed is coated onto a substrate and sintered,thereby forming the semiconductor layer made of the semiconductor finegrain, after that, ultraviolet rays are irradiated to the semiconductorlayer and, by using a photocatalyst effect of the semiconductor finegrain, an organic substance remaining in the semiconductor layer isremoved.

According to the sixth invention of the invention, there is provided anelectronic apparatus using a semiconductor layer made of semiconductorfine grain,

wherein an organic substance does not substantially remain in thesemiconductor layer.

The contents disclosed in conjunction with the first to third inventionsare also similarly applied to the fourth to sixth inventions so long asthey are not contradictory to the spirit of them. However, it is notalways necessary that the substrate on which the semiconductor layer isformed has the conductivity and the transparency in dependence on theapplication or function of the electronic apparatus.

Further, according to the seventh invention of the invention, there isprovided a manufacturing method of a semiconductor layer, whereby apaste in which semiconductor fine grain and a binder made of a polymercompound are mixed is coated onto a substrate and sintered, therebyforming the semiconductor layer made of the semiconductor fine grain,

wherein after the semiconductor layer is formed, ultraviolet rays areirradiated to the semiconductor layer and, by using a photocatalysteffect of the semiconductor fine grain, an organic substance remainingin the semiconductor layer is removed.

According to the eighth invention of the invention, there is provided asemiconductor layer made of semiconductor fine grain,

wherein a paste in which the semiconductor fine grain and a binder madeof a polymer compound are mixed is coated onto a substrate and sintered,thereby forming the semiconductor layer made of the semiconductor finegrain, after that, ultraviolet rays are irradiated to the semiconductorlayer and, by using a photocatalyst effect of the semiconductor finegrain, an organic substance remaining in the semiconductor layer isremoved.

According to the ninth invention of the invention, there is provided asemiconductor layer made of semiconductor fine grain,

wherein an organic substance does not substantially remain in thesemiconductor layer.

The contents disclosed in conjunction with the first to third inventionsare also similarly applied to the seventh to ninth inventions so long asthey are not contradictory to the spirit of them. However, it is notalways necessary that the substrate on which the semiconductor layer isformed has the conductivity and the transparency.

According to the invention constructed as mentioned above, the paste inwhich the semiconductor fine grain and the binder made of the polymercompound are mixed is coated and sintered, thereby forming thesemiconductor layer made of the semiconductor fine grain. After that, byirradiating the ultraviolet rays to the semiconductor layer, the organicsubstance remaining in the semiconductor layer is oxidization dissolvedby the photocatalyst effect of the semiconductor fine grain, becomescarbon dioxide, water, and the like, and is removed. Particularly, bysufficiently irradiating the ultraviolet rays, it is possible to realizethe state where the organic substance does not substantially remain inthe semiconductor layer. As disclosed in Non-Patent Document 2, if thesemiconductor fine grain is made of titanium oxide, the surface changesto the surface having hydrophilicity (the surface hydroxyl groupincreases), so that a binding force between the semiconductor fine grainincreases and the electron movement between the semiconductor fine grainbecomes easy. At the same time, if the semiconductor fine grain is madeof titanium oxide, a coupling force between the sensitizing dye and acarboxyl group is also increased due to an increase in surface hydroxylgroup. The electron movement between the dye and the semiconductor finegrain made of titanium oxide also becomes easy. Consequently, thephotoelectric conversion efficiency is improved.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross sectional view of a main portion of a dye sensitizedwet-type photoelectric conversion device according to an embodiment ofthe invention.

FIG. 2 is a cross sectional view of the main portion of the dyesensitized wet-type photoelectric conversion device according to theembodiment of the invention.

FIG. 3 is a schematic diagram showing a relation between a carboncomponent content of a semiconductor layer and an irradiating time ofultraviolet rays in the case where a paste in which titanium oxide finegrain and a binder made of a polymer compound are mixed is coated andsintered, thereby forming a semiconductor layer and, thereafter,ultraviolet rays are irradiated to the semiconductor layer in theembodiment of the invention.

FIG. 4 is a schematic diagram showing current/voltage curves of the dyesensitized wet-type photoelectric conversion device in the case wherethe paste in which the titanium oxide fine grain and the binder made ofthe polymer compound are mixed is coated and sintered, thereby forming asemiconductor layer and, thereafter, the ultraviolet rays are irradiatedto the semiconductor layer and in the case where the ultraviolet raysare not irradiated in the embodiment of the invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the invention will be described hereinbelow withreference to the drawings.

FIG. 1 shows a dye sensitized wet-type photoelectric conversion deviceaccording to an embodiment of the invention.

As shown in FIG. 1, in the dye sensitized wet-type photoelectricconversion device, an assembly obtained by forming a semiconductor layer2 (semiconductor electrode) made of semiconductor fine grain whichadsorbs dye and exhibits a photocatalyst activity onto a transparentconductive substrate 1 and a counter electrode obtained by forming aplatinum layer 4 onto a transparent substrate 3 are arranged so that thesemiconductor layer 2 and the platinum layer 4 face each other at apredetermined interval. An electrolyte layer (electrolytic solution) 5is sealed in a space between them. The electrolyte layer 5 is sealed bya predetermined sealing member (not shown). The semiconductor layer 2 isconstructed in such a manner that a paste in which semiconductor finegrain exhibiting the photocatalyst activity and a binder made of apolymer compound are mixed is coated onto the transparent electrode 2and sintered, further, ultraviolet rays are irradiated, an organicsubstance remaining in the semiconductor layer is removed, andthereafter, the sensitizing dye is adsorbed to the semiconductor finegrain.

FIG. 2 shows the dye sensitized wet-type photoelectric conversion devicein the case where, particularly, the transparent conductive substrate 1is a substance obtained by forming a transparent electrode 1 b onto atransparent substrate 1 a.

As a transparent conductive substrate 1 (or the transparent substrate 1a and the transparent electrode 1 b, a semiconductor layer 2 made of thesemiconductor fine grain, a transparent substrate 3, and an electrolytelayer 5, proper materials can be selected from those mentioned above asnecessary.

A manufacturing method of the dye sensitized wet-type photoelectricconversion device will now be described.

That is, first, the transparent conductive substrate 1 is prepared.Subsequently, a paste in which semiconductor fine grain exhibiting aphotocatalyst activity and a binder made of a polymer compound are mixedis coated onto the transparent conductive substrate 1 so as to have apredetermined gap (thickness) by a method such as doctor blade method,spin coating method, dip coating method, or the like. Then, thesemiconductor fine grain is sintered onto the transparent conductivesubstrate 1 by sintering it at a temperature of, for example, 400 to500° C. for a period of time of, for example, 30 minutes to 1 hour.Thus, the semiconductor layer 2 made of the semiconductor fine grain isformed on the transparent conductive substrate 1. Subsequently,ultraviolet rays are irradiated to the semiconductor layer 2 and anorganic substance remaining in the semiconductor layer 2 is dissolvedand removed by the photocatalyst effect of the semiconductor fine grain.After that, the semiconductor layer 2 is dipped into the dye solution orthe like, thereby allowing the dye to be adsorbed to the semiconductorfine grain. As such a dye, a proper one of those mentioned above can beselected as necessary.

On the other hand, the transparent substrate 3 is separately preparedand the platinum layer 4 is formed thereon.

The transparent conductive substrate 1 on which the semiconductor layer2 has been formed and the transparent substrate 3 on which the platinumlayer 4 has been formed are arranged in such a manner that thesemiconductor layer 2 and the platinum layer 4 face each other at apredetermined interval, for example, a distance of 1 to 100 μm,preferably, 1 to 50 μm. A space in which the electrolyte layer 5 issealed by using a predetermined sealing material is formed. Theelectrolyte layer 5 is injected into the space from an liquid injectionport which has previously been formed. After that, the liquid injectionport is closed. In this manner, the dye sensitized wet-typephotoelectric conversion device is manufactured.

The operation of the dye sensitized wet-type photoelectric conversiondevice will now be described.

The light which has entered from the transparent conductive substrate 1side by transmitting through the transparent conductive substrate 1excites the sensitizing dye adsorbed on the surface of the semiconductorfine grain of the semiconductor layer 2, thereby generating electrons.The electrons are promptly transferred from the sensitizing dye to thesemiconductor fine grain of the semiconductor layer 2. The sensitizingdye which lost the electrons receives the electrons from the ions of theelectrolyte layer 5. The ions which have given the electrons receivesthe electrons again in the platinum layer 4 of the counter electrode. Bysuch a series of processing steps, an electromotive force occurs betweenthe transparent conductive substrate 1 electrically connected to thesemiconductor layer 2 and the platinum layer 4. In this manner, thephotoelectric conversion is performed.

As mentioned above, according to the embodiment, the paste in which thesemiconductor fine grain exhibiting the photocatalyst activity and thebinder made of the polymer compound are mixed is coated onto thetransparent conductive substrate 1 and sintered, thereby forming thesemiconductor layer 2, and after that, by irradiating the ultravioletrays to the semiconductor layer 2, the organic substance remaining inthe semiconductor layer 2 can be removed by the photocatalyst effect ofthe semiconductor fine grain. Therefore, the binding between thesemiconductor fine grains in the semiconductor layer 2 is improved andthe electrons can be easily moved between the semiconductor fine grain,so that the photoelectric conversion efficiency is improved. Since it isunnecessary to raise the sintering temperature and extend the sinteringtime in order to reduce the residual amount of the organic substance inthe semiconductor layer 2, an increase in crystalline grain diameter canbe prevented. Thus, a decrease in specific surface area can beprevented. Such a situation that the state changes to the state with thecrystalline structure (in the case of titanium oxide, the rutile type)of the low photocatalyst activity is eliminated. The decrease inphotoelectric conversion efficiency can be prevented. Further, since thesintering temperature necessary to form the semiconductor layer 2 can besuppressed to a low temperature, a plastic substrate which is morereasonable in price and more flexible than a glass substrate can be usedas a transparent conductive substrate 1. In this manner, the reasonabledye sensitized wet-type photoelectric conversion device having excellentphotoelectric conversion characteristics for a long time, particularly,the dye sensitized wet-type solar cell can be realized.

The dye sensitized wet-type solar cell will now be described as anembodiment of the dye sensitized wet-type photoelectric conversiondevice.

The dye sensitized wet-type solar cell is manufactured as follows.First, 1.5 wT % polyethylene glycol is further mixed to the titaniumoxide paste and the resultant paste is stirred for one hour by a hybridmixer and degassed. After that, it is left for 24 hours, thereby forminga titanium oxide paste.

Subsequently, the obtained titanium oxide paste is coated onto a gap ofa size of 1 cm×1.5 cm and 175 μm of a fluorine doped conductive glasssubstrate having a sheet resistance of 15 Ω/cm² serving as a transparentconductive substrate 1 by the doctor blade method, and thereafter, thepaste is dried at 50° C. for 30 minutes. After that, it is held at 450°C. for 30 minutes, the titanium oxide is sintered onto the fluorinedoped conductive glass substrate, and the semiconductor layer 2 made ofthe titanium oxide fine grain is formed. A thickness of obtainedsemiconductor layer 2 is equal to about 13 μm.

The content of the organic in the semiconductor layer 2 made of thetitanium oxide fine grain obtained as mentioned above are measured by anEDS (Energy Dispersive X-ray Spectrum). Thus, an amount of organicsubstance (content of carbon (C) component) contained in thesemiconductor layer 2 is equal to about 1.4 atom %.

Subsequently, the ultraviolet rays are irradiated to the obtainedsemiconductor layer 2 made of the titanium oxide fine grain for about 70hours. The light source which was used is an extra-high pressure mercurylamp of 400 W. A change of the carbon component content of thesemiconductor layer 2 to the irradiating time of the ultraviolet rays isas shown in FIG. 3. It will be understood from FIG. 3 that the carboncomponent content which has initially been equal to 1.4 atom % decreasesgradually due to the photocatalyst effect of the titanium oxide with theelapse of the ultraviolet ray irradiating time, it is equal to 0.6 atom% or less by the irradiation of 5 hours, it is equal to 0.2 atom % orless by the irradiation of 10 hours, and almost of the carbon componentsin the semiconductor layer 2 are dissolved and extinguished (0.1 atom %or less) after the irradiation of 70 hours.

Subsequently, the device is dipped into a dehydrated ethanol solution inwhich cis-bis (isothiocyanate)-N,N-bis(2,2′-dipyridyl-4,4′-dicarboxylicacid)-ruthenium (II) dihydrate of 0.5 mM and deoxycholic acid of 20 mMare dissolved for 24 hours, thereby allowing the dye to be adsorbed intothe semiconductor layer 2.

On the other hand, lithium iodiode of 0.335 g, iodine of 0.0635 g,4-tert-butyl pyridine of 0.34 g, ethylene carbonate of 2.5 g, andpropylene carbonate of 2.5 g are mixed and stirred, so that theelectrolyte is obtained.

After the semiconductor layer 2 made of the titanium oxide fine grainadsorbing the dye is coated with the electrolyte, it is combined withthe platinum layer 4 formed on the transparent substrate 3 by thesputtering method so as to have a thickness of 100 nm, so that the dyesensitized wet-type solar cell is obtained.

Evaluation of the Photoelectric Conversion Efficiency

The photoelectric conversion efficiency is measured by a method wherebyan electric clip is connected to the fluorine doped conductive glasssubstrate as a transparent conductive substrate 1 in each dye sensitizedwet-type solar cell, an electric clip is connected to the transparentsubstrate 3 on which the platinum layer 4 has been formed, and a currentand a voltage generated when the light is irradiated to the dyesensitized wet-type solar cell are measured by a current/voltagemeasuring apparatus. Upon irradiation of the light, AM1.5 is used as alight source and light intensity on the dye sensitized wet-type solarcell is set to 100 mW/cm².

FIG. 4 shows measurement results of current/voltage curves in the casewhere the ultraviolet rays are irradiated to the semiconductor layer 2made of the titanium oxide fine grain and in the case where they are notirradiated. The measurement results of every four samples are shown. Itwill be understood from FIG. 4 that when the ultraviolet rays areirradiated to the semiconductor layer 2 made of the titanium oxide finegrain, the photoelectric conversion efficiency is increased to about4.4% from about 3.7 to 4.1%. It is considered that the reason why suchresults are obtained is that all of a short-circuit current, a releasevoltage, and a fill factor are increased.

It is considered that the reason why the photoelectric conversionefficiency is improved is that by irradiating the ultraviolet rays tothe semiconductor layer 2 made of the titanium oxide fine grain, theresidual organic substance is dissolved by the photocatalyst, so thatthe binding force between the titanium oxide fine grain is enhanced. Itwill be obviously understood that the process for irradiating theultraviolet rays to the semiconductor layer 2 made of the titanium oxidefine grain is valid means for improving the photoelectric conversionefficiency of the dye sensitized wet-type photoelectric conversiondevice.

Although the foregoing embodiment and example of the invention havespecifically been described above, the invention is not limited to theforegoing embodiment and example but many modifications based on thetechnical idea of the invention are possible.

For example, the numerical values, structures, shapes, materials, rawmaterials, processes, and the like mentioned in the foregoing embodimentand example are nothing but the examples and other numerical values,structures, shapes, materials, raw materials, processes, and the likedifferent from them can be also used as necessary.

As described above, according to the invention, the paste in which thesemiconductor fine grain and the binder made of the polymer compound aremixed is coated and sintered, thereby forming the semiconductor layermade of the semiconductor fine grain. After that, by irradiating theultraviolet rays to the semiconductor layer, the organic substanceremaining in the semiconductor layer is removed by the photocatalysteffect of the semiconductor fine grain. Thus, the residual organicsubstance in the semiconductor layer can be remarkably reduced. Bysufficiently irradiating the ultraviolet rays, it is possible to realizethe state where the residual organic substance does not existsubstantially. Therefore, the binding between the semiconductor finegrain in the semiconductor layer is improved and the electron movementbetween them becomes easy and the photoelectric conversion efficiency isimproved. since there is no need to raise the sintering temperature orextend the sintering time in order to reduce the residual amount of theorganic substance in the semiconductor layer, the decrease in thephotoelectric conversion efficiency can be also prevented. Since thesintering temperature necessary to form the semiconductor layer can besuppressed to a low temperature, the reasonable and flexible plasticsubstrate can be also used as a transparent conductive substrate or asubstrate. Consequently, the photoelectric conversion device havingexcellent photoelectric conversion characteristics, more generally, theelectronic apparatus having excellent characteristics can be obtained.

1. A method of manufacturing a photoelectric conversion device,comprising: coating a transparent conductive substrate with a pastecomprising a semiconductor fine grain and a binder made of a polymercompound; sintering the paste at a temperature of between approximately400° C. to 500° C. to form a semiconductor layer made of thesemiconductor fine grain, the semiconductor layer comprising an organicsubstance; and irradiating the semiconductor layer with ultraviolet raysfor between approximately 4 and 70 hours to remove at least some of theorganic substance in said semiconductor layer using a photocatalysteffect of the semiconductor fine grain.
 2. The method of claim 1,wherein the semiconductor fine grain comprises a plurality of kinds ofsemiconductor fine grain exhibiting photocatalyst activity.
 3. Themethod of claim 1, wherein said semiconductor fine grain having aphotocatalyst effect is made of titanium oxide, zinc oxide, or strontiumtitanate.
 4. The method of claim 1, wherein said polymer compound is apolymer compound having a viscosity improving effect.
 5. The method ofclaim 1, wherein said polymer compound is polyethylene glycol orpolystyrene.
 6. The method of claim 1, wherein irradiating thesemiconductor layer with ultraviolet rays for between approximately 4and 70 hours comprises irradiating the semiconductor layer withultraviolet rays for between approximately 10 and 70 hours.
 7. Themethod of claim 6, wherein irradiating the semiconductor layer withultraviolet rays for between approximately 10 and 70 hours comprisesirradiating the semiconductor layer with ultraviolet rays for betweenapproximately 30 and 70 hours.
 8. The method of claim 1, whereinirradiating the semiconductor layer with ultraviolet rays for betweenapproximately 4 and 70 hours comprises irradiating the semiconductorlayer with ultraviolet rays for a time sufficient to remove enough ofthe organic substance such that a content of a carbon component in saidsemiconductor layer after said irradiation by ultraviolet rays is equalto or less than 1 atomic %.
 9. The method of claim 8, whereinirradiating the semiconductor layer with ultraviolet rays for betweenapproximately 4 and 70 hours comprises irradiating the semiconductorlayer with ultraviolet rays for a time sufficient to remove enough ofthe organic substance such that the content of the carbon component insaid semiconductor layer after said irradiation by ultraviolet rays isequal to or less than 0.3 atomic %.
 10. The method of claim 1, whereinirradiating the semiconductor layer with ultraviolet rays for betweenapproximately 4 hours and 70 hours comprises irradiating thesemiconductor layer with ultraviolet rays for between approximately 50and 70 hours.
 11. The method of claim 10, wherein irradiating thesemiconductor layer with ultraviolet rays comprises irradiating thesemiconductor layer with ultraviolet rays for approximately 70 hours.12. The method of claim 1, wherein sintering the paste at a temperatureof between approximately 400° C. to 500° C. comprises sintering thepaste for between approximately 30 minutes and one hour.
 13. A method ofprocessing a semiconductor layer formed by sintering a paste coated on asubstrate, the paste comprising a semiconductor fine grain and a bindermade of a polymer compound, the method comprising: irradiating thesemiconductor layer with ultraviolet rays for approximately 70 hours.14. A method of manufacturing a semiconductor layer, comprising: forminga paste comprising a semiconductor fine grain and a binder made of apolymer compound; coating a substrate with the paste; sintering thepaste between approximately 400° C. and 500° C., thereby forming thesemiconductor layer comprising the semiconductor fine grain and anorganic substance, irradiating the semiconductor layer with ultravioletrays for between approximately 4 and 70 hours to remove, by using aphotocatalyst effect of said semiconductor fine grain, at least some ofthe organic substance in said semiconductor layer.